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B. Effectiveness The objective of the La Verkin Springs Unit was to develop a plan that would control the salt loading of the La Verkin Springs to the Colorado River. The present plan could remove over 95 percent of the salt from the springs. No other alternative, short of removing the entire flow of the springs from the river, proved more effective. The effectivness of reducing the salinity at Imperial Dam is somewhat less than the estimate made in the Final Environmental Statement - Colorado River Water Quality Improvement Program (INT-FES 77-15). This is due to the 22-year time of travel of a large part of water to a groun"d-water aquifer and then eventually reappearing in the Littlefield Springs of Arizona. This phenomenon delays the effect of the La Verkin Springs Unit at Imperial Dam. Assuming a first year operation of 1985, the reduction of salinity at Imperial Dam would be 7 mg/L in the beginning and 11 mg/L in years 22-50, and would continue through year 2035 which marks the end of the 50-year period of analysis. The annual equivalent of this reduction is 8" 4. mg/L for the 50 years. C . Efficiency The present plan is not considered cost effective. Total invest- ment costs are estimated to be $85 million. Economic analysis has shown the annual cost for each mg/L of salinity reduction at Imperial Dam to be about $1.06 million. Comparative cost estimates for some other salinity control projects range from about $200,000 to $450,000 per year. Table 2 shows an appraisal analysis comparison of the various desalting alternatives for the La Verkin Springs. The table readily shows that significant cost savings may be possible with higher recovery and optional pretreatment processes as well as brine deep well injection alternatives" The costs listed in Table 2 are based on October 1978 estimates and an interest rate of 6-7/8 per- cent. If construction is authorized, costs would reflect current interest rates . 002526 17